The present invention relates to a process for the dismutation of chlorosilanes, and more particularly a process for the dismutation of trichlorosilane and dichlorosilane.
Today the highest purity silicon for the semiconductor industry is almost always produced through the pyrolysis of a trichlorosilane-hydrogen mixture. In a variation, if dichlorosilane is used in place of trichlorosilane, much higher space/time yields are realized. Even the irreversible pyrolysis of monochlorosilane permits the production of high purity silicon with high space/time yields.
Dichlorosilane can also be used in organosilane chemistry for the production of diorganohalogen silanes of the type R.sub.2 SiCl.sub.2 through double hydrosilylization. Linear organopolysiloxanes may be obtained through chain extension reaction with these diorganosilanes, or, in the presence of functional groups in the organo-residue, three-dimensional, cross-linked polymers may be obtained through chain cross-linking reactions.
The dismutation of chlorosilane presents an especially favorable way to obtain dichlorosilane and monosilanes. Dichlorosilane is obtained through dismutation of trichlorosilane in the presence of a catalyst according to the following equation: EQU 2SiHCl.sub.3 .revreaction.SiH.sub.2 Cl.sub.2 +SiCl.sub.4.
Monosilane may be obtained catalytically through dismutation of dichlorosilane according to the following equation: EQU 3SiH.sub.2 Cl.sub.2 .revreaction.SiH.sub.4 +2SiHCl.sub.3.
Both reactions are equilibrium reactions; with an infinite reaction time an equilibrium occurs which depends only on temperature and the partial pressures of the reactants.
A large number of processes for the dismutation of chlorosilanes have been described in which the reaction was performed in the presence of a catalyst which is soluble in the chlorosilanes. It is also possible to perform the dismutation in a reaction medium which is miscible with the chlorosilanes and in which the catalyst is dissolved. But all these processes are noted for the disadvantages of the expensive and often difficult separation problems.
Therefore the art has used heterogenous catalysts which are insoluble in the chlorhydrosilicons. In Canadian Patent 1 184 017, Canadian Patent 1 162 028, German Patent 33 11 650, German Patent 25 07 864 and German Patent 21 62 537, for instance, the use of a slightly alkaline ion exchanger, AMBERLYST.RTM. A-21, is described, in which dimethylamino groups are bonded to a polystyrene structure. In European Patent A-206 621 the reaction product of tri-n-butylamine with the ion exchanger LEWATIT.RTM. SPC-118 is mentioned as a catalyst. The German Offenlegungsschrift 34 12 705 describes the use of a slightly alkaline anion exchanger with an aromatic heterocyclic base as a functional group.
The Japanese Patent 60/77120 A2 mentions the ion exchanger DUOLITE.RTM. ES-467 which contains amino and phosphoric acid groups for this purpose. DOE/JPL/955533-83/7 suggests the methylamine group-containing anion exchanger DOWEX.RTM. MWA-1 for this purpose. Finally, the European Patent A-138 669 also mentions alkaline ion exchange resins as catalysts.
All of these described processes agree in that ion exchangers based on organic polymers are used as heterogenous catalysts for the dismutation of chlorosilanes. However, these organic polymers do not have in any way ideal properties in regard to thermal and mechanical stability, inertness to chemical actions, accessibility of functional groups and solubility in the solvent used. Problems may therefore occur because either the organic matrix is not pressure- or temperature-resistant to the required extent or swells too much in the reaction medium used, is partially dissolved, or sticks together, or the functional groups are insufficiently or not at all accessible, or a relatively fast aminoseparation takes place.
It is the task of the invention to find catalysts for the chlorosilane dismutation reaction which do not have the disadvantages of the organic ion exchangers described above, and to create a suitable dismutation process using these catalysts.